Is there a reason why you think that this word should show up in this book? So far as I know, the word does not appear at any point in Guns, Germs, and Steel.

I have searched the book in a variety of ways and have not found any instance of this word in the book. I have searched in the Kindle version of the book. I have also searched the book using Amazon.com and Google books' search functions. In all cases, there were no hits for this word.

The word "infrastructure" refers to the resources needed for some (usually economic) activity. For example, we speak of roads, bridges, and electric lines as infrastructure because they are needed in order for our economy to function properly.

Infrastructure is not a concept that is particularly important to Diamond's argument in this book so I have no reason to believe that it appears in the book.